Mobile install woes - SWR and PEP

[etwalgade]

High SWR and Transmitted Power lower than expected.

What I have and how it's installed:
I have an older cobra radio (around 10 years old) its one of the cheaper ones, not the more expensive nice models, installed in my pickup truck. I have run the power directly to the battery. The Antenna is a FireStik FS-4BK 4' installed on the Bed Rail of my truck. I have also added an addition ground wire from the antenna mount to the truck body and confirmed it's grounded well. I do have it on one of those antenna springs so it won't break if it hits something. I am not using a whip because I park the truck in a carport with a 7' ceiling.

Problem:
I cannot seem to get my SWR lower than about 1.8 on 40 and 1.7 on 1. When I tested the radios power output, it's only reading about 2 of the expected 4 watts.

My Theories:
I suck at tuning
The radio is crap
Or I am using the wrong antenna or mount setup.

At any rate any help or ideas yall have would be great!

The radio receives just fine, I am picking up allot of skip from all over the South Eastern United States lately, but transmitting, not so good.

[MDYoungblood]

What is the SWR at channel 19 or 20, always give the middle of the band reading too.

3's

Greg

[etwalgade]

I think it was about 1.6, but I did not write it down.

[MDYoungblood]

Are you using a spring on the mount? The readings are giving me a clue that the antenna is too long. Where on the bed rail is the antenna located?

3's

Greg

[etwalgade]

I am using a spring, and I was wondering if that is contributing to the problem.
The Antenna is mounted about 6" to the rear of my toolbox which is mounted right behind the cab.

[MDYoungblood]

The spring is probably causing some of the SWR problem, close to the cab isn't helping either. Try removing the spring, you didn't state the size, shortening the antenna should bring the SWR down to an acceptable reading. You said you had a 102" whip, how was the SWR with it? You could always buy a couple antenna quick disconnects and use them on the antenna to switch them out easier. Can find them on eBay or Amazon.

3's

Greg

[etwalgade]

I don't have a whip, but its on my list of things to purchase after my next bout of amazon points come in.
I will pull the truck out and remove the spring from the equation and test. I will let you know what I find out.

[MDYoungblood]

The theory is that the antenna (FireStik) is designed to be mounted to a stud (the nut in this case), any added length would than need to be removed from the antenna's windings.
Now with that said most antennas are made long so they can be trimmed to adjust the SWR, be careful buying used antennas as they might have been trimmed too much.

3's

Greg

[etwalgade]

It was the spring. I now have a SWR of 1.02 on channel 1 and 1.04 on channel 40.

Unfortunately, this antenna is tunable only with a screw, which does not have enough travel to account for the spring. I had added the spring so it would just sort of bend out of the way and go back when backing under my car port. (Antenna is about 12" taller than the opening.


So... I am going to bite the bullet and get a whip.

[jessejamesdallas]

If you want to mount to bed rail, then mount it either behind or right over where the rear wheel is, on the drivers side of the truck....

As long as you have a decent ground to the antenna mount, you should see SWR drop like a rock...

Closer to the cab you get, the higher the antenna needs to be mounted...I have mine on a riser I made out of some old scrap 1" square tubing I had laying around...SWR 1.0 to 1.1 across the band...